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Power Supply Fusing questions

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hey all, I am working on my basic power supply diagram. My question is mainly regarding things like the VTC solenoids for use on the VG30DETT Nissan Engine. I am using a flying lead harness for the EMU Black, and am wondering if the solenoids need to be through a relay and fuse with ground controlled by the ECU? Assuming that goes through the enable power supply? Attached what I have thus far for nitpicking and such.

Attached Files

i would normally give the injectors their own relay and the coils a separate relay and add the vct to the relay you current have them going to and yes run a fuses to it if you wise but i don't normally worry,

Gotcha! Time to amend the drawing. Injectors and coils separate. And a fuse not necessary, but also not against the law. Thank you for the reply.

Amended... I am trying not to run a ton of relays as the main body harness is now residing with the ECU in the passenger footwell area. Since the injectors do not draw a ton of amperage, I am assuming this would suffice. I am always open to suggestions. Getting prepared to drop in the engine and start measuring for wiring and such! Super excited about it all really.

Attached Files

Just had a quick glance at your wiring diagram, looks clean, good job!

Currently your relay 2 pin 86 is connected to the Aux Output of the ECU and there's and a constant ground at pin 85. The EMU Black Aux Outputs are in fact switched grounds. So you will need to give the relay 2 pin 86 12v+ and connect the Aux Output of the ECU to pin 85.

Also, I'm assuming the "Ecu Excite" for relay 3 & 4 will be a switched 12v+? If yes, relay 3 & 4 are correctly wired.

I see in your component list that you have your crank angle sensor and a flex fuel sensor listed, but you haven't take it into account in your 12V power supply diagram. They will need to get a 12v+ supply.

Finally, it's usually better to have the fuse as close to the battery as possible, so I try to use one fuse for what the relay will control (so I put the fuse before pin 30) instead of having one fuse per actuator after the relay. I don't know what fuse / relay box you will use, but I would recommend the Bussmann, they pretty great and easy to populate, very versatile.

I am picking up what you are laying down. I am assuming that you do some actual math to get the size of the cumulative load on the other side of the relay? I have been looking at the bussman setups, and simplifying the fuse situation would definitely make that more fitting. Thank you for the input. I will amend and go from there!

Calculating the cumulative load is important for your wire sizing too. But if you did a good job at sizing your wires, the fuse is there to protect it in case something goes wrong. Like in the event of a short, you don't want your wiring to melt or act as a incandescent filament, you want the fuse to blow. But obviously you don't want it to blow under normal conditions. This is why PDMs are so great, you can monitor the current in the normal operating conditions and you can program protection accordingly.

So short answer, yes, you will need to take your cumulative load into account and size your fuse accordingly, without being too close to your normal condition so it doesn't blow without any "real" reasons.

Awesomesauce. Thank you Frank. I appreciate the help!